Catalytic substrates are well known in the art and vary from solids to liquids and, more particularly, to fabric type substrates. The invention, in preferred embodiments, is directed to this latter type of catalytic substrate, and in a further preferred embodiment, to such catalytic substrates that can be used for carrying out catalytic chemical vapor deposition at high temperatures, especially temperatures in excess of 1200° F. At such temperatures, most catalytic substrates become unsuitable. Some such substrates will simply burn or melt, while other such substrates will lose the necessary physical properties required to function as a catalytic substrate. The present invention provides such catalytic substrates that can function at temperatures of 1200° F. and greater, while maintaining sufficient physical properties to function as a catalytic substrate. Therefore, the present substrate is capable of carrying out chemical reactions at elevated temperatures, especially chemical vapor depositions temperatures, such as that in producing nano tubes, especially carbon nano tubes.
High temperatures substrates that are formed of high temperature particulate ceramics are capable of sustaining such chemical vapor deposition reaction temperatures, but the reaction products are spaced at relatively far apart positions, because of the relatively large particulate size of the catalytic substrate, e.g. 100 mesh particles and the like.
Therefore, in order to provide very closely spaced loci for such catalytic reactions, the general approach in the art is to provide a porous substrate, generally a nonwoven, fibrous substrate, in which finely divided particulate solid catalyst can be dispersed. With such dispersion of finely divided particulate material, the loci of the catalytic reaction can be very closely spaced apart. Thus, the distance between the products of the catalytic reaction can be quite small, and filters, for example, made of such substrates can filter very small particles. This approach is quite satisfactory for many catalytic reactions, but some catalytic reactions, such as chemical vapor depositions for forming carbon nano tubes, require high temperatures, generally in excess of 1200° F. Accordingly, the substrate must be capable of sustaining those temperatures in order to carry out the catalytic reaction.
It is known that single layered substrates of carbon or ceramics in conventional form, e.g. fabrics, felts, cloths, tows, et cetera, may be used as substrates for catalyzed, high temperature vapor deposition growth of “whiskers” of materials such as carbon, silicon carbide and titanium nitride thereon for improving filters made of those conventional forms, such as disclosed in U.S. Pat. No. 6,390,304. However, such single layered conventional substrates are merely treated with a solution of a precursor of the catalyst that is reduced to catalytic form. As such, there is no controlled deposition of the catalyst particles, and the “whiskers” are generally randomly displayed with greatly varying distances therebetween.
Thus, the art simply has not provided such porous substrates, made of nonwoven fibrous materials, that are capable of carrying uniformly dispersed, finely divided, particular solid catalyst and which can also sustain temperatures in excess of 1200° F. Of course, substrates of that nature would be of considerable value to the art.